The polytope underlying the cone \({\rm pos}(A)\)  is
the product \(\Delta _{d_1-1} \times \Delta _{d_2-1}\)  of two simplices.
The triangulations of pos(A) are studied in
[1]}. The toric variety \(T_A\)  is the
cone over the Segre variety \(\mathbb {P}^{d_1-1} \times \mathbb {P}^{d_2-1}\) .
Its points are the
\(d_1 \times d_2\)  matrices of rank \(\le 1\) .
The prime ideal of \(T_A\)  is generated by the
\(2 \times 2\)  minors of
a \(d_1 \times d_2\)  matrix; see
[2]}.
The positive variety \(T_A^+\)  represents the independence model
for distributions on \([d_1]\)  and \([d_2]\) .
We know from Proposition REF  that the linear map \(A\) 
identifies \(T_A^+\)  with the cone \({\rm pos}(A)\) .
